Should You Derive from `std::string`?

Is Derivation from std::string Class a Misguided Practice?

In Effective C , it is advised against deriving from the std::string class primarily because it lacks a virtual destructor. This disposition has prompted some confusion regarding the specific requirements for a class to be suitable as a base class.

Contrary to the assumption that a class must be eligible for inheritance to serve as a non-polymorphic base class, C offers alternative mechanisms for code reuse. For instance, private inheritance can facilitate mixins or aspect-oriented programming, while public inheritance is exclusively designated for polymorphic scenarios.

The prevalent reason for discouraging derivation from std::string lies in the distinction between value types and reference types in C . Unlike in Java and C#, C classes are value types, meaning that value-by-value copies are performed during inheritance operations. Consequently, the slicing problem arises when the derived class has a different memory footprint from the base class, resulting in unexpected behavior and potential inconsistencies.

To alleviate this issue, non-member and non-friend functions should be prioritized for extending functionality. If inheritance is considered necessary, composition or template metaprogramming should be employed instead to avoid the pitfalls associated with slicing.

In summation, deriving from std::string is not recommended due to its lack of a virtual destructor and the inherent complexities associated with value-type inheritance in C .

Prevention of Non-Polymorphic Usage

If a base class is solely intended for code reuse and not for polymorphic purposes, there is no straightforward mechanism to prevent clients from instantiating derived classes directly through pointers or references. However, leveraging static_assert or type traits techniques can provide runtime checks to detect non-conforming usage.

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